Matter and ChangeI. Nature of Science

DHS Chemistry

A. What is Chemistry?

Science is the use of evidence to develop testable explanations and predictions of natural phenomena.

A. What is Chemistry?

• Chemistry is the study of matter and its changes

______ is defined as the amount of matter in

something.

mass

• You can use a _______ to take the mass of an object.

• Note: Mass is not the same as ______.

balance

weight

–Weight is mass times the gravitational acceleration, 9.8m/s2.

–Mass will not change if you go to the moon.

Volume–the amount of space something occupies.

Gas occupies space

Matter

• Matter is defined as anything that has _____ and ________

massvolume

Matter vs. Non-Matter

Matter

• Your Desk

• Air

• H2O

Non-Matter

• Light

• Photons

Matter and ChangeII. MatterDHS Chemistry

Remember,

Matter is anything that has mass and volume.

A. Properties of Matter

A physical property is a quality or condition of a substance that can be observed or measured without changing the substance.

Example: color, size, shape, density, melting and boiling points

• A chemical property refers to a substance’s ability to undergo a chemical reaction and form new substances. In order to observe a chemical property you must change the substance.

• EX: toxicity, flammability, reactivity

Intensive Properties

An intensive property is one that does not depend on amount.

EX: density, boiling point, melting point

Extensive Properties

An extensive property is one that depends on amount (how much you have).

EX: mass, volume

Practice1. Determine whether the following are

physical or chemical properties:

a) sulfur is yellow

b) sulfur will combine with iron to form iron sulfide.

c) copper is a good conductor of heat.

physical

Chemical

physical

Practice2. Determine whether the following describes

intensive or extensive properties:

a) I have 1 gram of water

b) Water’s freezing point is 0 °C

c) Liquid H2O has a heat capacity of 1 J/g °C

extensive

intensive

intensive

B. States of Matter

3 states of matter exist commonly on earth

SOLID LIQUID GAS

(aq) = aqueous

Aqueous refers to a solid that is dissolved in water

All matter expands when heated and the particles that make up all matter have motion.

Solids• Definite shape

• Definite volume

• No (significant) expansion on heating

• No (significant) compressibility

• Has low energy

• Low viscosity

• High density (for most substances)

• Fixed particles

Liquids• Indefinite shape

• Definite volume

• slight expansion on heating

• No (significant) compressibility

• Has moderate energy

• Medium to high viscosity

• Medium density (for most substances)

• Particles slide past each other

Gas• Indefinite shape

• Indefinite volume

• Extensive expansion on heating

• Extensive compressibility

• Has high energy

• high viscosity

• low density

• Fast and continuous motion

Gases are also considered fluid since it flows

LIQUID GASSOLID

Viscosity

• Viscosity is the resistance to flow. High viscosity means it flows slower, or the substance is viscous

• Ex. Honey has a high viscosity

You can decrease viscosity by increasing the heat

Density: the ratio of mass to volume

• formula is: Density = mass/volume

• Typical units include: g/mL, g/cm3, or any unit for mass/any unit for volume

• Changes when the state of matter changes

Density: the ratio of mass to volume

• Is an intensive property, therefore doesn’t change when the amount changes

• Less dense objects will float, and dense objects will sink

• Water has a density of 1 g/mL or 1 g/cm3

C. Classification of Matter

All matter can be classified into 2 types:

There are two types ofPure Substances

Elements Compounds

1. Pure Substances

can be either elements (i.e. Al or H2) or compounds (i.e. H2O, CO2)

Elements are the simplest forms of matter and consist of atoms of all one type (EX: H2, S8, C)

>how do you know if it’s an element?<

• Elements can be found on the periodic table

An atom is a single unit of an element that retains all the properties of that element.

(ex. Al has 1 atom of Aluminum and S8 has 8

atoms of sulfur)

Gold vs. Carbon

More on pure substances

• Compounds are two or more atoms chemically bonded together in a set ratio and are shown using a chemical formula. (EX: H2O, C12H22O11 ) The subscript indicates the number of atoms of that element.

•Compounds are formed when elements chemically combine and consist of molecules (H2O) or formula units (NaCl)

Molecules & formula units

• A molecule (for molecular compounds) or formula unit (for ionic compounds) is the smallest part of a compound that retains all the properties of the compound

• Compounds have a definite composition.

(EX: H2O is always 89% Oxygen and 11% Hydrogen)

Chemical Separation

• pure substances can only be chemically separated, they cannot be physically separated.

Compounds

• substances in a compound lose their individual properties and take on a new set of properties

Compound

• If you take water, H2O, and add another oxygen to it you now have H2O2, hydrogen peroxide, a completely new substance with complete new properties.

Water Hydrogen peroxide

Oxygen+ =

Compound

• If you take Carbon Dioxide, CO2, and take an oxygen away from it you get Carbon monoxide, CO, a very dangerous and lethal gas.

Carbon dioxide - oxygen = carbon monoxide

2. Mixtures• a mixture is a physical blend of

substances

• The composition of mixtures can vary

2. Mixtures• mixtures can be physically

separated

• Elements retain their individual properties

Mixtures

• Lemonade… a mixture of water, sugar and lemon juice

• If you add more water you still have lemonade

• If you add more sugar, you still have lemonade

Types of physical separation: picking out, distillation,

chromatography, using a magnet, filtration, boiling off a liquid

Fractional Distillation

Chromatography

Two types of Mixtures:

Homogeneous Heterogeneous

1. Homogeneous Mixtures

• appear to have a uniform composition (look the same throughout)

(disguises itself as a pure substance)

• also known as solutions

• a solution can be any combination of solids, liquids, or gases

• Ex. salt water, brass

Homogeneous Mixture

an alloy is the special term for a solid solution of 2 or more metals. Ex. Brass, sterling silver, stainless steel

Homogeneous Mixtures

2. Heterogeneous mixtures --- do not appear to have a uniform composition

• Includes suspensions and colloids

EX: salads, oil and water, milk

What goes in the black boxes?

practice

1. Determine whether the following are pure substances or mixtures.

a) concrete

b) ice cream

c) NH3

d) potassium fluoride

Mixture

Mixture

Pure Substance

Pure Substance

2. Identify the following as atoms, molecules, compounds, elements. Two terms may fit.

a) F2

b) Xec) CCl4d) H2SO4

Element / molecule

Element / atom

Compound / molecule

Compound/molecule

More Practice

Pennies(97.5% Zinc, 2.5% Copper)

Category 1Category 2Category 3

SolidMixturehomogeneous

More Practice

Orange Juice with Pulp

Category 1Category 2Category 3

LiquidMixtureheterogeneous

More Practice

Baking Soda

NaHCO3

Category 1Category 2

Category 3

SolidPure substanceCompound

More Practice

Oxygen

O2

Category 1Category 2

Category 3

gasPure substanceelement

More Practice

Sterling Silver(92.5% pure silver and 7.5% other metals)

Category 1

Category 2

Category 3

SolidMixturehomogeneous

The truth about Gold

18K gold

Category 1Category 2Category 3

SolidMixturehomogeneous

Matter and ChangeIII. Changes in MatterDHS Chemistry

A. Physical vs Chemical

• a __________change alters a substance without changing its chemical composition ; it is reversible

EX: phase changes, cutting, crushing, dissolving

H2O(s) + heat H2O(l)ice + heat water

Solid liquid

physical

All Phase changes are physical

All Phase changes are physical

WaterVapor

LiquidWater

Ice

Boiling vs Evaporation

• There are two types of vaporization: boiling (throughout a liquid) and evaporation (at a surface)

a) Gas to liquid (condensation)b) Liquid to gas (vaporization)

Pictures of Phase Changes

A. Physical vs Chemical

a chemical change occurs when a substance (or substances) changes into new substances; it is not reversible.

EX:rusting, burning, odor forming

Changes in Matter

• Physical Change- alter or change the form or appearance of a substance without changing the material into a new substance

• Chemical Change: A change in matter that creates a new substance with new properties

PracticeClassify the following as a physical change or chemical change:

a) Ice Melts• Changing from

one phase to another is a Physical Change… with water, no matter solid, liquid, or gas, it is still H2O

b) Chopping wood

Chopping wood just changes the appearance, but its still wood

c) Sugar dissolves in tea

• Sugar in tea can be separated by boiling off the water to leave the sugar behind

d) Nail rusting

• The iron reacts to the Oxygen in the air causing the formation of rust (Ferric Oxide)

e) Silver tarnishing

• Metals such as copper, brass, silver, aluminum reacts with the oxygen in the air and causes it to tarnish

d) Milk Curdling

• The proteins in Milk will hydrolyze, (react with the water) and eventually come together and form curds, this is how cheese is made

B. Chemical Reactions

• A chemical reaction occurs when a new substance has been formed

• this is shown typically by a chemical equation

Ex.

Mg + 2HCl H2 + MgCl2--reactants-- ---products---

How to Identify a Chemical Change

• Not all Chemical Changes are easy to see, here are some ways to determine if you have a chemical change.

signs of a chemical reaction (and more)

Formation of a Gas (bubbles)

• Sometimes when two substances come in contact a reaction occurs producing a gas.

Forming of a solid (precipitate)• If you combine

some substances, a reaction can occur forming a solid called a precipitate

Change of Color

• Some substances, when combined, will turn another color

Change in Temperature

• When some chemicals react they either give off energy and get hotter (exothermic reaction) or use energy and get cooler (endothermic reaction)

Formation of Sparks

• When sodium is placed in water, the reaction is so violent a fire results

Creates an odor

Law of Conservation of Mass

During any chemical change, the total amount of matter remains the same

<Mass can not be created nor destroyed>

Law of Conservation of mass

this means in any chemical reaction, the total mass of the reactants must equal the total mass of the products

reactants products

64 + 192 = 152 + ?

Think of the yields symbol, , as an = sign, and make sure the masses are equal on both sides

104 g

C. Energy Changes

Heat is a form of energy, and energy is defined as the ability to do work (that is, to exert a force and move something)

Potential Energy

• Chemical bonds store energy. This is known as chemical potential energy

• all substances possess chemical potential energy (the energy stored in atoms and molecules)

during chemical reactions, energy may be released or absorbed. But just as with mass, the total amount of energy of a system before the reaction must equal the total amount of energy of a system after the reaction.

When a reaction gets hotter or colder, this means energy is being transferred from one substance to another. The energy may take on a different form (eg. Light). Remember, energy can not be created or destroyed

Law of Conservation of Energy

Energy can not be created or destroyed

It simply changes form

C. Energy Changes

• a process that releases energy is ____________

• The surroundings will get warm• The particles slow down

• EX: water ice + heat

exothermic

Exothermicfeels warm to the touch

Endothermic Reactions• a process that absorbs energy is

___________ • The surroundings will get cool• The particles speed up

• EX: ice + heat water

endothermic

Endothermicfeels cool to the touch

Practicea) Steam condensing

Condensing =

gas liquid

Do I need heat? Or do I take heat out of it (cool it down?)

Practiceb) dry ice subliming

Subliming =

Solid gas

Do I need heat? Or do I take heat out of it (cool it down?)

Practice

1. Determine whether the following processes are endothermic or exothermic.

a) steam condensing

b) dry ice subliming

c) burning wood

d) NH4Cl + heat NH4+ + Cl-

e) opening a cold pack

exothermic

exothermic

endothermic

endothermic

endothermic